Twitter as big as it is, is just a website across millions of others. In the mobile app market there is exactly two companies, Apple and Google, that's it.
Does Oppo or Samsung has any power when publishing an app? No? Then they are not part of this market.
https://www.apple.com/services/ https://www.apple.com/logic-pro/ https://www.apple.com/final-cut-pro/
Of course, these are not the bread and butter products.
I find it a bit pointless to separate their hardware and software. I know few people who run Windows or Linux on their Apple hardware. For me, Apple is primarily a products company that excels in fusing hardware and software together. They are increasingly expanding into services, too.
And similarly again there's none you can buy from Oppo and Samsung (I'll consider the Samsung store negligible in terms of market share).